1. Field Of The Invention
The present invention relates to a method and apparatus for generating individual droplets of ink in a printer device.
2. The Prior Art
A number of developments have been made in piezo-ceramic elements for use as drive elements for the ejection of individual droplets of ink in printer apparatus. Such drive elements typically have the form of piezo-electric plates or piezo-electric tubes. In the former, a piezo-electric plate forms a wall of an ink chamber which is connected to one side to an ink rersevoir and at its other side, to a discharge jet. When the plate is electrically driven, a volume change occurs in the ink chamber, due to a mechanical change in shape of the plate, with the volume change resulting in the ejection of a droplet. Such an apparatus is shown in German Pat. No. OS 2,132,082. In the latter case, the piezo-electric tube embraces a part of a tubular ink channel which is connected between a reservoir and a discharge jet. When the tube is energized, a pressure wave is generated inside the ink channel which results in the ejection of a droplet.
It is also known to design piezo-electric drive elements in a comb form as shown in German Pat. No. AS 2,527,647. The free ends of the comb teeth are allocated to discharge openings such that a droplet is ejected from an opening when its associated tooth is electrically driven.
Other developments have employed piezo-ceramic materials. However, the handling and processing of piezo-ceramic materials is difficult and time consuming. Moreover, processes using piezo-ceramic materials are relatively costly, because the positioning of drive elements relative to each other in a print head require extreme precision. In addition, problems occur in connection with the selection of individual drive elements. A slight modification in the structure of a piezo-ceramic element resulting from change in the ambient temperature or change in the ink composition requires individual balancing of each individual drive element.
Accordingly, it is desirable to provide an apparatus and method for increasing the simplicity of design and construction of piezo-ceramic elements, and reducing their costs.